1. Field of the Invention
The present invention relates generally to compositions having multiple responses to excitation radiation. In particular, the invention relates to compositions having a first response to a first electromagnetic radiation and, after intermediate exposure to a second electromagnetic radiation, a second response to the first electromagnetic radiation, different from the first response.
2. Discussion of Background Information
Conventional luminescent materials have one response (e.g., emission) to a given excitation by electromagnetic radiation. Luminescent materials may, for example, convert one wavelength to a second wavelength whether ultraviolet to visible, ultraviolet to infrared, visible to visible, visible to infrared, infrared to infrared, or infrared to visible. Luminescent materials may also emit near the wavelength they absorb.
The need exists for luminescent materials that can controllably emit different responses, e.g., emissions, to a single energy source. Such materials may be employed, for example, in security and laser applications. Luminescent materials with more than one response can also be employed as switches, e.g., in which a first response to excitation radiation may be controllably switched to a second response to the same excitation radiation by non-destructive and non-invasive means. This may be useful, for example, in optical computing, communication (switches and amplifiers), imaging, sensing and detection. However, conventional luminescent materials, as described above, emit only a single response to a single energy source or are not permeable (e.g., changeable). The need therefore exists for luminescent materials that provide more than one response to a single energy source.